1. Field of the Invention
The present invention relates to a re-connection method for a communication network system which permits a multicast connection (multipoint connection) with a plurality of subscribers which are accommodated by a plurality of ATM (Asynchronous Transfer Mode) switches in a B-ISDN (Broadband Integrated Services Digital Network).
2. Related Arts
Currently, a B-ISDN (Broadband Integrated Services Digital Network) adoption that employs the ATM (Asynchronous Transfer Mode) technique is expected to constitute the next generation communication network. The ATM method is one whereby digital data to be transmitted are divided into data set having a constant length of 48 bytes, control data called a 5-byte header is added to the individual digital data sets, and the resultant data are transferred by hardware switching.
FIGS. 56A and 56B are diagrams showing a connection form for a B-ISDN. A B-ISDN permits communications not only while using the one-to-one connection, as in a conventional telephone network, as is shown in FIG. 56A, but also while using a multipoint connection shown in FIG. 56B whereby the same data can be transmitted to a plurality of locations.
Specifically, in FIG. 56A is shown a one-to-one connection between a subscriber a-Sub accommodated by a station A which is an ATM switch and a subscriber b-Sub accommodated by a station B which is an ATM switch. In FIG. 56B is shown a multipoint connection among a subscriber a-Sub accommodated by the station A, subscribers b-Sub and c-Sub accommodated by the station B, and subscribers d-Sub and e-Sub accommodated by a station C which is an ATM switch.
In a case where, due to insufficient bandwidth, a busy line or no response, at least one of the subscribers (subscribers b-sub, c-Sub, d-Sub and e-Sub in FIG. 56B) with whom the multipoint connection is requested, can not be connected with the subscriber (subscriber a-Sub) which is requesting the multipoint connection, conventionally the transmission of data keeps waiting until a connection with the pertinent subscriber can be established. Therefore, the transmission of data to subscribers which are ready to receive will be delayed.
Further, if data are transmitted even though there is a subscriber with whom a connection had not been established, the multipoint connection must be re-established after the transmission of data is terminated in order to send data to the specific subscriber. At this time, if a request for the multipoint connection is issued again, the same data again transmitted to the subscribers which have already received those data. This is a very uneconomical process.
It is, therefore, one object of the present invention to provide a re-connection method, for a communication network system which permits a multipoint connection, that ensures an efficient processing when there is a subscriber with whom a connection is not established for the multipoint connection, and also to provide a switch therefor.
To achieve the above object, according to a first aspect of the present invention, there is provided a re-connection method for a communication network system that enables a multipoint connection by which the same data is transmitted from a first subscriber accommodated in a first switch to a plurality of second subscribers accommodated in a second switch, the method comprising the steps of:
transmitting the data by the second switch to at least one of the second subscribers connected with the second switch;
re-transmission requesting by the second switch to the first switch for re-transmitting of the data to the at least one of the second subscribers; and
re-connection requesting by the first switch to the second switch for re-connecting the at least one of the second subscriber which has not connected with the second switch.
According to a second aspect of the present invention, there is provided the re-connection method according to the first aspect, wherein the first switch stores information of the subscriber which has not connected with the second switch; and
in the step of re-connection requesting, the first switch transmits the information to the second switch, and the second switch processes to connect to the subscriber based on the information.
According to a third aspect of the present invention, there is provided the re-connection method according to the first aspect, wherein the second switch stores information of the subscriber which has not connected with the second switch; and
in the step of re-connection requesting, the second switch processes to connect to the subscriber based on the information.
According to a forth aspect of the present invention, there is provided the re-connection method according to the first aspect, wherein a database of the communication network system stores information of the subscriber which has not connected with the second switch; and
in the step of re-connection requesting, the first switch access to the database to obtain the information and transmits the information to the second switch, and the second switch processes to connect to the subscriber based on the information.
According to a fifth aspect of the present invention, there is provided the re-connection method according to the first aspect, wherein a database of the communication network system stores information of the subscriber which has not connected with the second switch; and
in the step of re-connection requesting, the second switch accesses to the database to obtain the information, and the second switch processes to connect to the subscriber based on the information.
According to a sixth aspect of the present invention, there is provided the re-connection method according to the first aspect, further comprising the step of:
re-transmitting the data to the second switch for the subscriber connected with the second switch, which has not connected with the second switch.
According to a seventh aspect of the present invention, there is provided the re-connection method according to the sixth aspect, the step of re-connection requesting is processed after completion of transmitting the data by the transmitting step; and
in the re-transmitting step, the second switch transmits the data to the subscriber connected with the second switch, which has not connected with the second switch.
According to a eighth aspect of the present invention, there is provided the re-connection method according to the sixth aspect, wherein the first switch stores the data; the step of re-connection requesting is processed during transmitting the data by the transmitting step; and
in the re-transmitting step, the first switch transmits the data to second switch for the subscriber connected with the second switch, which has not connected with the second switch during the transmitting the data by the transmitting step.
According to a ninth aspect of the present invention, there is provided the re-connection method for a communication network system that enables a multipoint connection by which the same data is transmitted from a first subscriber accommodated in a first switch to a plurality of second subscribers accommodated in a second switch, the method comprising the steps of:
transmitting the data by the second switch to at least one of the second subscribers connected with the second switch; storing the data in the second switch;
requesting for re-connection by the second switch to at least one of the second subscribers which has not connected with the second switch; and
re-transmitting the data stored in the second switch to the subscriber connected with the second switch, which has not connected with the second switch.
According to a tenth aspect of the present invention, there is provided the re-connection method for a communication network system that enables a multipoint connection by which the same data is transmitted from a first switch to a second switch and a third switch, the method comprising the steps of:
transmitting the data to subscribers connected with the second and third switch, which are accommodated in the second and third switch respectively;
re-transmission requesting by the second switch to the first switch for re-transmitting the data to at least one of the second subscribers which has not connected with the second switch;
transmitting a notice that there is no subscriber which has not connected with the third switch from the third switch to the first switch; and
re-connection requesting by the first switch to the second switch for re-connecting with at least one of the second subscribers which has not connected with the second switch.
Other features and advantages of the present invention will become rapidly apparent from the following description when taken in conjunction with the accompanying drawings.